1. Field of the Invention
The present invention relates to an electromagnetic drive type flow control valve, suitably used in an air conditioning apparatus for an automobile, using hot water for a heating operation.
2. Description of Related Art
A co-pending U.S. patent application No. 856,985 filed on Mar. 24, 1992 proposes an air conditioning (heating) apparatus for an automobile provided with an internal combustion engine, wherein a heater core is arranged in an air duct, and the heater duct is connected to an engine cooling water line for receiving hot water that is subjected to a heat exchange with the air flow in the duct for heating the air discharged to the cabin. An electromagnetic drive control valve is arranged in the passageway of the hot water from the engine for controlling the flow of water and the temperature of the air as discharged. The control valve is constructed by a body defining valve seats, valve members for cooperating with the valve seats, and a solenoid connected to the valve members for controlling the flow of water between the engine cooling water line and the heater core.
As is well known, engine cooling water includes foreign substances, such as a sand, dust and sludge. Therefore, a seal member is provided between a valve shaft and the body for preventing foreign substances in the engine cooling water in the valve body from being introduced into the space inside the solenoid. The space inside the solenoid is, however, in communication with a water flow passageway via a vent opening formed in the valve rod therethrough. The vent passageway is for equalizing the pressure between the space inside the solenoid and the flow passageway. The equalization of the pressure can ensure movement of the valve by a relatively small electromagnetic force generated by the actuator. Thus, a certain amount of foreign substance in the flow passageway can be introduced into the space in the solenoid via the vent passageway in the valve rod, causing the sliding parts, such as the core of the solenoid, to stick.
According to the present invention, an electromagnetic valve device is provided for controlling the flow of a fluid, comprising:
a housing defining therein a passageway for the fluid; PA1 a valve rod having at least one valve member movably arranged in the housing for controlling the flow of the fluid in said passageway; PA1 a solenoid mechanism that includes a moving part connected to the valve rod for obtaining a repeated movement of said valve member for a desired stroke, and a stational part for generating an electromagnetic force for moving said moving part; PA1 the solenoid mechanism having a chamber, the volume of which varies in accordance with the movement of said moving part; PA1 a seal member made of a flexible material arranged between the valve rod and the housing so that said first chamber is sealed with respect to the passageway; PA1 means for defining a second chamber, the volume of which chamber is increased upon a stroke movement of the valve rod for decreasing the volume of the first chamber and is decreased upon a stroke movement of the valve rod for increasing the volume of the first chamber, and; PA1 means for obtaining the communication of a fluid between the first and second chambers for equalizing the pressure of the communication fluid between the first and second chambers.